To encourage co-operative play, ArenaNet has implemented a matching system to bring high-level characters in line with their beginner friends.
The sidekick system was detailed at the Guild Wars 2 panel at PAX, as reported by Gamespot, and will see high level characters dropped down to the party average but still permitted to harvest experience and rewards.
This allows character of all levels to play together without unbalancing game events, negating the need for secondary characters or alts when you're ahead of your mates.
Interestingly, ArenaNet also discussed a loot system which sees players rewarded with tokens rather than pieces of equipment. These tokens can be swapped for class-appropriate equipment of the player's choice, so nobody feels gypped by an inappropriate random drop.
ArenaNet seems to have been quite focussed on how Guild Wars 2 will encourage group play, again emphasising the game's rejection of the "holy trinity", and discussing participation rewards for all players.
No release date has been set for Guild Wars 2, but a beta is expected soon.